1. Field of the Invention
The present invention is generally directed to measuring the relative angular orientation of one surface to another surface. In particular, the invention is especially useful for measuring the angular orientation of two nearly parallel roll surfaces. The invention can be adapted to absolute measurement relative to a fixed reference provided one of the surfaces is at a known reference orientation. The two surfaces are assumed to be in a side by side arrangement rather than in line with each other.
2. Discussion of the Prior Art
Methods to measure roll to roll parallel alignment have been described in previous patents and patent applications. In U.S. Pat. No. 6,628,378 by Marangoni, et al., a two frame invention indicates whether two rolls are oriented in a parallel alignment condition. A laser on one frame projects a light beam to a second frame with a target. On the second frame, the position of laser beam on the target indicates whether the rolls are in a parallel aligned condition. A second laser beam and second target orients the two frames correctly for accurate measurement.
There are some limitations with this method. The two laser beams must be projected perpendicular to the first surface. The use of a secondary visual target with crosshairs for positioning of the two frames longitudinally to each other does not provide highly accurate positioning. Longitudinal positioning errors directly affect the angular measurement readings and reduce the measuring accuracy of the parallel orientation. Laser beam divergence and thermal drift present additional accuracy problems. In actual use, it is frustrating to rotationally and longitudinally orient the two frames correctly to obtain a precise reading. A separate calibration frame is used to check the alignment of the laser and optics.
In patent application Ser. No. 10/802,338 by Loen, two frames are mounted on two surfaces where the angular orientation of the two surfaces is to be measured. The distance between defined points on the two frames is used to measure the angular orientation. Measuring errors can be difficult to control when the surfaces are a large distance apart.